The invention relates to a passive magnetic position sensor, comprising a substrate with a resistance network which is arranged on this substrate and is assigned a contact spring structure, which can be deflected under the action of a permanent magnet, with electrical connection between the resistance network and the contact spring structure being established by contact which is dependent on the position of the permanent magnet, the contact spring structure and the resistance structure being enclosed in a sealed housing and the permanent magnet being movable outside the sealed housing.
Such a position sensor is known from DE 196 48 539. The resistance network and the contact structure are in this case arranged on a substrate. A magnetic device which is connected to a movable object, the position of which is to be determined, causes the contact spring structure to be deflected in such a way that it contacts the resistance network and an output signal corresponding to the position of the moved object can be picked up at the position sensor.
A magnetic position sensor of the type described is only a few centimeters long. To permit reliable operation of the position sensor, the magnet therefore cannot be increased in size without any limit, since this would have the consequence that many spring legs of the contact spring structure are simultaneously attracted by the magnet, with the result that the output signal of the sensor no longer provides unequivocal signals and is consequently no longer usable.
The invention is consequently based on the object of providing a passive magnetic position sensor with improved magnetic force of the permanent magnet.
According to the invention, the object is achieved by the permanent magnet being polarized in the direction of movement of the contact spring structure, a flux guiding device for concentrating the force of attraction of the undisturbed magnetic field being arranged near the permanent magnet.
The invention has the advantage that, on account of the flux guiding body, the pattern of the undisturbed magnetic field is changed to such an extent that its gradient is increased in the direction transverse to the housing. The magnetic field formed by the permanent magnet in which no housing with a resistance network and contact spring structure is introduced is considered as the undisturbed magnetic field. On the basis of this measure, the force of the magnetic field can be intensified without the geometrical dimensions having to be changed.
A simple development of the invention is that the flux guiding device is formed as a magnetically permeable cap which can be fitted onto the permanent magnet. Such a cap has a u-shaped cross section, at the free ends of which virtual magnetic poles form. Consequently, the undisturbed magnetic field (field in the air) is concentrated to such an extent that a considerable increase in the field gradient can be achieved transversely to the direction of the sensor housing at the position of the housing.
In another refinement, the flux guiding device comprises two additional auxiliary magnets, the permanent magnet being arranged between the two auxiliary magnets and the direction of magnetization of the auxiliary magnets being opposed to the direction of magnetization of the permanent magnet.
The magnetic force of the permanent magnet can in this case be utilized particularly fully if the housing is nonmagnetically formed and consequently the forces act undamped on the contact spring structure.